Neurovascular congruence results from a shared patterning mechanism that utilizes Semaphorin3A and Neuropilin-1

Peripheral nerves and blood vessels have similar patterns in quail forelimb development. Usually, nerves extend adjacent to existing blood vessels, but in a few cases, vessels follow nerves. Nerves have been proposed to follow vascular smooth muscle, endothelium, or their basal laminae. Focusing on the major axial blood vessels and nerves, we found that when nerves grow into forelimbs at E3.5-E5, vascular smooth muscle was not detectable by smooth muscle actin immunoreactivity. Additionally, transmission electron microscopy at E5.5 confirmed that early blood vessels lacked smooth muscle and showed that the endothelial cell layer lacks a basal lamina, and we did not observe physical contact between peripheral nerves and these endothelial cells. To test more generally whether lack of nerves affected blood vessel patterns, forelimb-level neural tube ablations were performed at E2 to produce aneural limbs; these had completely normal vascular patterns up to at least E10. To test more generally whether vascular perturbation affected nerve patterns, VEGF(165), VEGF(121), Ang-1, and soluble Flt-1/Fc proteins singly and in combination were focally introduced via beads implanted into E4.5 forelimbs. These produced significant alterations to the vascular patterns, which included the formation of neo-vessels and the creation of ectopic avascular spaces at E6, but in both under- and overvascularized forelimbs, the peripheral nerve pattern was normal. The spatial distribution of semaphorin3A protein immunoreactivity was consistent with a negative regulation of neural and/or vascular patterning. Semaphorin3A bead implantations into E4.5 forelimbs caused failure of nerves and blood vessels to form and to deviate away from the bead. Conversely, semaphorin3A antibody bead implantation was associated with a local increase in capillary formation. Furthermore, neural tube electroporation at E2 with a construct for the soluble form of neuropilin-1 caused vascular malformations and hemorrhage as well as altered nerve trajectories and peripheral nerve defasciculation at E5-E6. These results suggest that neurovascular congruency does not arise from interdependence between peripheral nerves and blood vessels, but supports the hypothesis that it arises by a shared patterning mechanism that utilizes semaphorin3A.     

应用振动训练可修复小鼠肌肉疲劳损伤

为探讨不同强度全身振动训练对于生物体运动表现、运动疲劳以及生理生化反应的影响。本研究使用4周大雄性C57BL/6J小鼠为模型,随机分作3组,每组8只动物:无振动训练对照组(sedentary control,SC);相对较低强度振动训练组(5.6 Hz/0.13 g; relative low-intensity vibration, LV);相对较高强度振动训练组(13 Hz/0.68 g; relative high-intensity vibration, HV)。振动训练以每天振动15 min,每周5次,为期4周,随后进行各项测试包括:前肢抓力、衰竭性耐力运动测验、疲劳生化指标分析、临床血液生化检测以及病理组织切片观察。数据以单因素方差进行分析,并以Duncan's test检验不同的组间是否存在显著差异。两组接受振动训练介入的小鼠比对照组,具有显著提升肌力和衰竭性耐力运动的时间。在疲劳与肌肉损伤相关生化指标部分,振动训练具有明显降低单次运动测试后血氨与血乳酸浓度以及肌酸激酶活性上升的作用。在临床血液生化方面,4周振动训练显著降低草醋酸转胺酶、麸丙酮酸转胺酶与肌酸激酶活性,以及尿素氮浓度。本研究证实振动训练4周的连续介入下,具有提升运动表现与抗疲劳的作用,而且不会造成健康小鼠在生理生化以及病理上的副作用。在提供一般健康成人的运动训练指导上,全身振动训练具有健康促进的应用性。     

Comparative myology of the forelimb of Liolaemus sand lizards (Liolaemidae)

The lizard genus Liolaemus includes numerous constituent clusters of putatively related taxa, one of which is the Liolaemus boulengeri group, which in turn includes the sand lizards (of the Liolaemus wiegmannii subgroup). Members of the sand lizard group exhibit three different modes of burying into sand. The general morphology of the forelimb muscles of those Liolaemus species is analysed. Herein, we present a study of the forelimb musculature of all species considered by Halloy et al. (1998). This study has three principal goals. First, we are seeking myological characters that will be useful in formulating phylogenetic hypothesis about the species of Liolaemus. With these characters, we also wish to compile morphological data that represent the morphological space implied in the diverse locomotor behaviours of these animals. Second, we are looking for derived features that reflect functional changes in the use of forelimb. Third, we wish to provide a cladistic analysis that can be used to test phylogenetic hypothesis derived from other sources of data. We present 48 characters in a data set and analyse it cladistically. We obtained a hypothesis of relationships of the Liolaemus species and compared this with previous hypotheses based on other characters. The trees obtained are not congruent with previously proposed phylogenies. We were unable to identify in our trees nodes that are based on structures reflecting functional changes in the use of the forelimb. The morphological similarities in the forelimb musculature of all species analysed seems to conform a very conservative general anatomical pattern with which Liolaemus sand lizards perform most of their locomotor behaviours.     

Unconstrained 3D-kinematics of prehension in five primates: Lemur,capuchin, gorilla,chimpanzee, human

Primates are known for their use of the hand in many activities including food grasping. Yet, most studies concentrate on the type of grip used. Moreover, kinematic studies remain limited to a few investigations of the distal elements in constrained conditions in humans and macaques. In order to improve our understanding of the prehension movement in primates, we analyse here the behavioural strategies (e.g., types of grip, body postures) as well as the 3D kinematics of the whole forelimb and the trunk during the prehension of small static food items in five primate species in unconstrained conditions. All species preferred the quadrupedal posture except lemurs, which used a typical crouched posture. Grasp type differed among species, with smaller animals (capuchins and lemurs) using a whole-hand grip and larger animals (humans, gorillas, chimpanzees) using predominantly a precision grip. Larger animals had lower relative wrist velocities and spent a larger proportion of the movement decelerating. Humans grasped food items with planar motions involving small joint rotations, more similar to the smaller animals than to gorillas and chimpanzees, which used greater rotations of both the shoulder and forearm. In conclusion, the features characterising human food prehension are present in other primates, yet differences exist in joint motions. These results provide a good basis to suggest hypotheses concerning the factors involved in driving the evolution of grasping abilities in primates.     

Hox C6 expression during development and regeneration of forelimbs in larval Notophthalmus viridescens

 A central theme concerning the epimorphic regenerative potential of urodele amphibian appendages is that limb regeneration in the adult parallels larval limb development. Results of previous research have led to the suggestion that homeobox containing genes are ”re-expressed” during the epimorphic regeneration of forelimbs of adult Notophthalmus viridescens in patterns which retrace larval limb development. However, to date no literature exists concerning expression patterns of any homeobox containing genes during larval development of this species. The lack of such information has been a hindrance in exploring the similarities as well as differences which exist between limb regeneration in adults and limb development in larvae. Here we report the first such results of the localization of Hox C6 (formerly, NvHBox-1) in developing and regenerating forelimbs of N. viridescens larvae as demonstrated by whole-mount in situ hybridization. Inasmuch as the pattern of Hox C6 expression is similar in developing forelimb buds of larvae and epimorphically regenerating forelimb blastemata of both adults and larvae, our results support the paradigm that epimorphic regeneration in adult newts parallels larval forelimb development. However, in contrast with observations which document the presence of Hox C6 in both intact, as well as regenerating hindlimbs and tails of adult newts, our results reveal no such Hox C6 expression during larval development of hindlimbs or the tail. As such, our findings indicate that critical differences in larval hindlimb and tail development versus adult expression patterns of this gene in these two appendages may be due primarily to differences in gene regulation as opposed to gene function. Thus, the apparent ability of urodeles to regulate genes in such a highly co-ordinated fashion so as to replace lost, differentiated, appendicular structures in adult animals may assist, at least in part, in better elucidating the phenomenon of epimorphic regeneration. Received: 6 November 1998 / Accepted: 12 December 1998     

DIFFERENCES IN THE TIMING OF PRECHONDROGENIC LIMB DEVELOPMENT IN MAMMALS: THE MARSUPIAL–PLACENTAL DICHOTOMY RESOLVED

In contrast to placentals, marsupials are born with forelimbs that are greatly developmentally advanced relative to their hind limbs. Despite significant interest, we still do not know why this is the case, or how this difference is achieved developmentally. Studies of prechondrogenic and chondrogenic limbs have supported the traditional hypothesis that marsupial forelimb development is accelerated in response to the functional requirements of the newborn's crawl to the teat. However, limb ossification studies have concluded that, rather than the forelimb being accelerated, hind limb development is delayed. By increasing the taxonomic coverage and number of prechondrogenic events relative to previous studies, and combining traditional phylogenetic analyses of event sequences with novel analyses of relative developmental rates, this study demonstrates that the timing of limb development in marsupials is more complex than commonly thought. The marsupial phenotype was derived through two independent evolutionary changes in developmental rate: (1) an acceleration of the forelimb's first appearance and (2) a delay of hind limb development from the bud stage onward. Surprisingly, this study also provides some support for an evolutionary acceleration of the marsupial hind limb's first appearance. Further study is needed on the developmental and genetic mechanisms driving these major evolutionary transitions.     

Restraint of Fgf8 signaling by retinoic acid signaling is required for proper heart and forelimb formation

Cardiomelic or heart–hand syndromes include congenital defects affecting both the forelimb and heart, suggesting a hypothesis where similar signals may coordinate their development. In support of this hypothesis, we have recently defined a mechanism by which retinoic acid (RA) signaling acts on the forelimb progenitors to indirectly restrict cardiac cell number. However, we still do not have a complete understanding of the mechanisms downstream of RA signaling that allow for the coordinated development of these structures. Here, we test the hypothesis that appropriate Fgf signaling in the cardiac progenitor field downstream of RA signaling is required for the coordinated development of the heart and forelimb. Consistent with this hypothesis, we find that increasing Fgf signaling can autonomously increase cardiac cell number and non-autonomously inhibit forelimb formation over the same time period that embryos are sensitive to loss of RA signaling. Furthermore, we find that Fgf8a, which is expressed in the cardiac progenitors, is expanded into the posterior in RA signaling-deficient zebrafish embryos. Reducing Fgf8a function in RA signaling-deficient embryos is able to rescue both heart and forelimb development. Together, these results are the first to directly support the hypothesis that RA signaling is required shortly after gastrulation in the forelimb field to temper Fgf8a signaling in the cardiac field, thus coordinating the development of the heart and forelimb.     

Substrate alters forelimb to hindlimb peak force ratios in primates

It is often claimed that the walking gaits of primates are unusual because, unlike most other mammals, primates appear to have higher vertical peak ground reaction forces on their hindlimbs than on their forelimbs. Many researchers have argued that this pattern of ground reaction force distribution is part of a general adaptation to arboreal locomotion. This argument is frequently used to support models of primate locomotor evolution. Unfortunately, little is known about the force distribution patterns of primates walking on arboreal supports, nor do we completely understand the mechanisms that regulate weight distribution in primates. We collected vertical peak force data for seven species of primates walking quadrupedally on instrumented terrestrial and arboreal supports. Our results show that, when walking on arboreal vs. terrestrial substrates, primates generally have lower vertical peak forces on both limbs but the difference is most extreme for the forelimb. We found that force reduction occurs primarily by decreasing forelimb and, to a lesser extent, hindlimb stiffness. As a result, on arboreal supports, primates experience significantly greater functional differentiation of the forelimb and hindlimb than on the ground. These data support long-standing theories that arboreal locomotion was a critical factor in the differentiation of the forelimbs and hindlimbs in primates. This change in functional role of the forelimb may have played a critical role in the origin of primates and facilitated the evolution of more specialized locomotor behaviors.     

Forelimb regeneration in thyroidectomized adult newts following organ culture and autografting of the thyroid glands

Summary Thyroidectomy and organ culture of adult newt thyroid glands three days prior to forelimb amputation was followed by autografting the glands subcutaneously into the animal's lower jaw region 9, 18 or 25 days postamputation (GC^{9, 18, 25} day series). This was an attempt, utilizing 515 animals, to elucidate further the role of the thyroids in regeneration. Amputated limbs of the thyroidectomized (Thx) and autografted muscle explant (MC = sham) cases underwent stumping or were significantly delayed in their regeneration rate and displayed abnormal morphogenesis compared with control regenerates. In the GC⁹ series newts, regenerates were identical to controls 45 days postamputation. However, regenerates of the GC¹⁸ series cases exhibited delayed and abnormal development at 45 days; but they were not as delayed and had fewer abnormalities than those cases in the Thx and MC groups. Results of the GC²⁵ series newts were similar to those of the Thx group. Within 5 days of autografting the thyroids, epidermal moulting resumed and long-term survival ensued. We conclude that normal limb regeneration in the adult newt is thyroid hormone(s) dependent, specifically the later stages of growth, differentiation and morphogenesis.Supported by grant A-1208 from the Natural Sciences and Engineering Research Council of Canada to R.A.L.